• Communications of the Korean Mathematical Society
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• v.23 no.2
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• pp.211-227
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• 2008

As a mathematical model proposed to understand the behaviors of interacting species, cross-diffusion systems with functional responses of prey-predator type are considered. In order to obtain $W^{1_2}$-estimates of the solutions, we make use of several forms of calculus inequalities and embedding theorems. We consider the quasilinear parabolic systems with the cross-diffusion terms, and without the self-diffusion terms because of the simplicity of computations. As the main result we derive the uniform $W^{1_2}$-bound of the solutions and obtain the global existence in time.

• Bulletin of the Korean Mathematical Society
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• v.41 no.2
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• pp.371-385
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• 2004

In this paper, we investigate the uniqueness of positive solutions to weak competition models with self-cross diffusion rates under homogeneous Dirichlet boundary conditions. The methods employed are upper-lower solution technique and the variational characterization of eigenvalues.

• The Journal of Society for e-Business Studies
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• v.17 no.2
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• pp.115-127
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• 2012

The diffusion of the mobile telecommunication service in a country could be affected by the diffusions of the services in her neighbor countries. Previous studies on the diffusions of the telecommunication service among countries have been mainly focussed on the comparison after individual diffusion estimation. However, it would be natural to think the diffusion of the mobile telecommunication service in one country could affect to and be affected by the diffusion of the mobile telecommunication service in her neighbor country. In this study, we have applied the multinational diffusion model to model the crossnational effect in the diffusion of the mobile communication service in China, Korea, U.S., Japan, and Hong Kong. Among these 5 countries China is the latest country to adopt the mobile communication service, and we were interested in whether the diffusion of the mobile communication service in Korea, U.S., Japan, or Hong Kong has affected the diffusion of the mobile communication service in China or not. In our application result, the diffusion of the mobile communication service in China has been affected significantly by those in all of the 4 neighbor countries.

• Journal of Information Management
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• v.37 no.1
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• pp.1-16
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• 2006

Due to the dramatic development of the Internet, the ICT market has changed from a voice based services to data based services. Substitution and complementary dynamism has emerged from communication technology services such as the Internet, mobile phone, and telephone. This paper analyses diffusion patterns of communication technologies such as the Internet, cellular phones, and telephones in different country groups. We estimate modified logistic growth model using time series data for the years 1975-2002. As a result, it is possible to categorize country groups according to the patterns of diffusions. This research creates essential information to forecast demand for new services based on incumbent services as well as provide information on strategies for entering the network industry.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.4
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• pp.48-56
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• 1999

In this paper, we have investigated experimentally the effects of initial oxygen concentration on oxygen pileup phenomenon and the diffusion of implanted impurities. 1.2 MeV $^{11}B^{+}$ and 2.2 MeV $^{31}P^{+}$ ions were implanted into p-type (100) Si wafers with a dose of 1${\times}10^{15}$ / $\textrm{cm}^2$. Secondary ion mass spectrometry(SIMS) measurements were carried out to obtain depth distribution profiles for implanted impurities and oxygen atoms after two-step annealing of $700^{\circ}C$(20 hours)+$1000^{\circ}C$(10 hours). Residual secondary defect distribution and annealing behabiour were also studied by cross-sectional transmission electron microscopy(TEM) observations. Oxygen pileup nearly $R_p$(projected range) were observed by SIMS measurements and considerable amount of residual secondary defect layer were observed by TEM observations. It can be seen that oxygen atoms are trapped at the secondary defects by the experimental results. Enhanced diffusions of boron and phosphorus to the bulk direction were observed with the increasing of initial oxygen concentration.

• Journal of the Korean Geographical Society
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• v.51 no.1
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• pp.167-184
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• 2016

This paper investigates the migration process of Korean population in Northeastern China since the 19th century, focusing on the population distribution patterns in different time periods which reflect changes and diffusions of diaspora space. Korean migration into Northeastern China seemed to begin from the late 19th century, and can be classified into four different periods including cross-border refugee period (19th to 1910), political exile period(1911-1931), forced migration period(1932-1945), and economic-driven migration period(after 1946). The Korean migration into Northeastern China was closely related to paddy field rice farming by Korean migrants, which can be interpreted as a process of contagious diffusion starting from border area between Korea and China at the early stage. And then, process of hierarchical diffusion occurred along with urban centers on the railways from the 1930s. At the later stage, Korean migration has extended to coastal urban centers, other big cities in China and other countries including Korea since the 2000s. Recently, ethnic Korean communities in China have experienced changes from rural village based community to urban district based community as well as from single-nuclei ethnic structure around Northeastern China toward multi-nuclei ethnic structure extending to coastal urban areas in China.